Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$5.72	12.198%	$6.4177	$6.42	$6.40	$6.40
Purchase #2	$84.90	12.303%	$95.3452	$95.35	$95.35	$95.30
Purchase #3	$35.94	9.205%	$39.2483	$39.25	$39.25	$39.20
Purchase #4	$7.28	13.315%	$8.2493	$8.25	$8.25	$8.20
Purchase #5	$249.30	8.221%	$269.795	$269.80	$269.80	$269.80
Purchase #6	$30.64	3.160%	$31.6082	$31.61	$31.60	$31.60
Purchase #7	$184.74	6.278%	$196.338	$196.34	$196.35	$196.30
7 purchase totals =	$598.52		$647.0017	$647.02	$647.00	$646.80